Organic and polymeric materials with large pi-electron delocalization are known to exhibit a nonlinear optical response, which, in many cases, is larger than that of inorganic materials. Of particular importance for organic materials is the origin of the nonlinear response in the polarization of the delocalized pi-electron cloud as opposed to displacement or rearrangement of nuclei found in inorganic materials as discussed in A. F. Garito, J. R. Heflin, K. Y. Wong, and O. Zamami-Khamiri, "Nonlinear Optical Properties of Polyenes: Electron Correlation and Chain Conformation" in Nonlinear Optical Properties of Polymers, Materials Research Society Symposium 109, A. J. Heeger, J. Orenstein, and D. R. Ulrich, Eds., Materials Research Society, pp. 91-102 (1988).
Nonlinear optical properties of organic and polymeric materials are well known and described in 1) F. Kajzar and J. Messier, "Cubic Effects in Polydiacetylene Solutions and Films" in Nonlinear Optical Properties of Organic Molecules and Crystals, D. S. Chemla and J. Zyss, Eds., Academic Press, Inc., Orlando, Fla., 2, 51-83, (1987) and 2) P. N. Prasad, "Design, Ultrastructure, and Dynamics of Nonlinear Optical Effects in Polymeric Thin Films" in Nonlinear Optical and Electroactive Polymers, P. Prasad and D. Ulrich, Eds., Plenum Press, New York, 41-67 (1987).
Theory and practice of nonlinear optical processes which occur by means of third order optical susceptibility, .chi..sup.(3) (chi-3), including intensity dependent refractive index, optical bistability, optical frequency conversion, degenerate four wave mixing, and optical phase conjugation, have potential utility in such diverse applications as optical communications, integrated optics, optical signal processing, optical sensor protection, and optical logic, and are discussed in G. Stegeman, C. Seaton, R. Zanoni, Thin Solid Films, 152, 231-263 (1987); D. M. Pepper, "Nonlinear Optical Phase Conjugation", Optical Engineering, 21, 156-183 (1982); and the reference of Kajzar and Messier (supra).
A recent patent useful as background for third order nonlinear optical properties is U.S. Pat. No. 4,796,976.
It is known in the art that thin films of organic and polymeric materials with large optical nonlinearities in combination with silicon-based electronic circuitry have potential applicability to laser modulation and deflection, information control in optical circuitry, and the like.
Conventional thrust of materials research and development for the above stated applications has been to provide a microscopically polarizable molecule or molecular segment with extended electron delocalization through conjugated pi-bonds such as are found in large, planar benzenoid hydrocarbons. Unfortunately, materials containing such extended electron delocalization suffer from attendant light absorption, severely limiting both transmission of light and available bandwidth. Furthermore, the materials are often insoluble in organic liquids and intractable, and as such, are not processable into useful device forms.
Specifically, third order nonlinear optical responses have been reported for crystals of an organic material where stacked molecules in the crystal indicate some form of intermolecular interaction [P. G. Huggard, W. Blau, and D. Schweitzer, Appl. Phys. Lett., 51, (26) pages 2183-2185, (1987)]. Organic charge transfer complexes formed from organic molecules with delocalized pi-electrons such as perylene and pyrene and electron accepting molecules, such as tetracyanoethylene and tetracyanoquinodimethane are discussed in T. Gotoh, T. Kondoh, K. Egawa, and K. Kubodera, Nonlinear Optical Properties of Materials, 1988 Technical Digest Series 9, pp. 7-10, Optical Society of America, Washington, D.C., 1988. These complexes were examined as powders owing to the intractable nature of the materials. Powder measurements of third order susceptibilities for these complexes are larger than those reported for the highest values obtained for state of the art polymers.
The nature of resonant third order optical nonlinearity derived from photogeneration of charge carriers in a polymer composite photoconductor, consisting of poly(N- vinylcarbazole) and trinitrofluorenone, was disclosed by P. N. Prasad et al. in "Resonant Nonlinear Optical Processes and Charge Carrier Dynamics in Photoresponsive Polymers", Mol. Cryst. Liq. Cryst., 160, 53-68 (1988). This publication describes various poly(N-vinylcarbazole) and trinitrofluorenone compositions and coatings whose third order susceptibility was determined by degenerate four wave mixing. In the reference, third order nonlinear optical effects derive from the response of photogenerated electron-hole pairs in a photoconductor. Absorption of light at the resonant frequency of this photoconductor is essential to the generation of these electron-hole pairs which are responsible for the nonlinear optical properties of the medium.
A background reference relating to use of charge transfer complexes in photoconductors is W. D. Gill, "Polymeric Photoconductors", Photoconductivity and Related Phenomena, J. Mort and D. M. Pai (Eds.), Elsevier Scientific Publishing Company, NY, 303-334 (1976). The function of the charge tansfer complex is to provide a molecular system where optical excitation at visible wavelengths generates an electrical charge which is used to neutralize an impressed electric charge in an imagewise fashion.
The concept of charge transfer in donor-acceptor complexes in general is discussed in C. K. Prout and J. D. Wright, Angew. Chem. Int. Ed., 7 (9), 659-667 (1968), and in R. S. Mulliken and W. B. Person, Molecular Complexes, Wiley Interscience, New York, 1-32, 1969.
Radiation curable polymers having pendant ethylenically unsaturated peptide groups are disclosed in U.S. Pat. No. 4,378,411.